-- Because of the {2, 7} appearing in row 3 and in column 8, there must be a hidden pair {2, 7} in the top right 3x3 box, in r1c7 & r2c7.

-- The other hidden pair is harder to spot. First, notice the "1" at r1c6 and the "3"s at r1c9 and r2c2. Clearly neither "1" nor "3" can appear at r1c5 or r2c5. {1, 3} can't fit in at r4c5 either, because of the {1, 3} in r4c1&2. Finally, because of a row on block interaction we can infer that the {1, 3} in row 5 must fall in the middle right 3x3 box (that is, in r5c7-9) because row 6 is already filled in that box. So there can't be a "1" or a "3" in r5c5. We can conclude, then, that the pair {1, 3} must occupy r6c5 & r8c5.

With this step completed you should be able to find the triplet {1, 3, 4} in r6c4-6, leaving only the pair {7, 9} to occupy r6c1&2 ... the rest should be fairly simple. dcb

I found the 1,3 pairing in row 6 but could not determine if 4 or 7 was the third partner. It turns out to be a 4, but without knowing that, a 7 in r6c2 is not the logical choice as the next hint suggests.